It has been brought to our attention that Killing Floor has updated for all clients, with a full, free, new Portal-themed prototype level. This is a complete, fully-functional level, but was not yet due for release. While we are investigating the source of the leak, everyone who owns Killing Floor is welcome to explore the new level and let us know what you find! We suspect that this may be part of the bedlam that has been going on since Potato Fool's Day.
Screenshots may be found here!
As a heads up it seems The Ball has also been infected: